This Netpage system involves the interaction between a user and a computer network (or stand alone computer) via a pen and paper based interface. The ‘pen’ is an electronic stylus with a marking or non-marking nib and an optical sensor for reading a pattern of coded data on the paper (or other surface).
The Netpage pen is an electronic stylus with force sensing, optical sensing and Bluetooth communication assemblies. A significant number of electronic components need to be housed within the pen casing together with a battery large enough to provide a useful battery life. Despite this, the overall dimensions of the pen need to be small enough for a user to manipulate it as they would a normal pen.
If the Netpage pen has a ballpoint nib, the ink cartridge must be kept as small as possible to conserve space within the pen casing, yet not so small that it needs to be replaced too frequently. Furthermore, the force sensor is best located at the end of the cartridge axially opposite the nib. This effectively precludes retracting the cartridge through the top (non-writing end) of the pen without disassembling much of the pen.
Beyond the Netpage context, most ink pens have cartridges that need to be inserted or withdrawn through the ends of the tubular pen casing. This imposes structural restrictions of the shape of the cartridge and therefore its ink storage capacity.